The invention relates to a focussing condition detector, and more particularly, to a focussing condition detector in which light impinging upon an imaging surface of the detector is subject to a photoelectric conversion to derive a signal which is evaluated according to a given formula by way of an arithmetic operation, the result of which is utilized to indicate an in-focus or out-of-focus condition.
A focusing condition detector is known in which light from an object being photographed which impinges upon an imaging surface is electrically detected by a photoelectric transducer element and then converted into digital form for arithmetic operation, the result of which is utilized to indicate a focussing condition or to drive an imaging lens into a position corresponding to an in-focus condition. In such an arrangement, a blur between the detector and the object being photographed and electrical noise as well as their quantization errors all contribute to the total noise. This causes unnecessary concern and inconvenience to a user since a display element which is used to indicate a focussing condition may flash and flicker in a boundary region between an in-focus and an out-of-focus condition or the lens is continually oscillated by an associated drive motor over a very limited range, resulting in a failure to fix its position.